In clutches for PTOs on tractors and other utility vehicles, clutch plates or disks are frictionally engaged. This friction generates heat and excessive heat can cause premature clutch wear and failure. For this reason, many tractors use hydraulically engaged wet clutches wherein cooled and filtered hydraulic oil flows through the clutch assembly. The cooling oil flows through the clutch continuously while the clutch is engaged. However, energy is wasted if cooling oil flows through the PTO clutch assembly while the clutch is disengaged.
U.S. Pat. No. 4,540,078 entitled Clutch Lube Control relates to a hydraulic control circuit that temporarily increases flow of cooling and lubrication oil when the PTO clutch changes from a disengaged to an engaged state. A lube valve moves to an increased flow position for a certain time period after engagement of the PTO clutch.
PTO clutches for tractors and other utility vehicles may be activated by hydraulic oil pressure moving a clutch piston to shift plates and disks into fractional engagement. A pressure regulating valve may be provided between the main hydraulic circuit and the clutch piston. Pressure spikes may occur in the main hydraulic circuit (i.e., from turning the steering wheel to the stops), and the pressure regulating valve prevents them from reaching the clutch piston. Dedicated circuits with specific pressure settings are used to prevent pressure spikes from reaching the clutch piston.
A PTO clutch is needed that does not require a dedicated circuit to shut off lubrication oil to the PTO clutch when the clutch is disengaged. A PTO clutch is needed that does not require a dedicated circuit to limit pressure spikes in the clutch activation pressure from reaching the clutch piston. A PTO clutch is needed that provides these advantages with a simplified hydraulic circuit for supplying oil to the clutch.